1. Field of the Invention
The invention relates to a low friction radial and thrust bearing assembly for rotationally supporting machine shafts relative to side frames of, for example, a food cutting machine.
2. Related Technology
Food cutting machines of various types are utilized to cut, slice, dice and otherwise reduce the size of larger food products into smaller size pieces that can be utilized by the food processing industry or other end users. One type of food cutting machine utilizes rotary disk blades mounted on a spindle that in turn is supported by a drive shaft that extends through side frames of the machine between which the spindle carrying the cutting blades is located.
The rotary cutting blades may cooperate with fixed stripper teeth extending between the blades requiring the blades to be precisely aligned between the stripper teeth with a minimum of side play. Other rotary cutting blades may be mounted on a spindle assembly and supported by a shaft or shafts extending through machine side frames wherein the blades likewise must be supported between the machine side frames with a minimum of end play between the ends of the cutter blade spindles and the side frames.
During operation of the cutting blades, the spindles and drive shaft or shafts supporting the spindles must be supported relative to the side frames by bearing assemblies that must accommodate both radial and thrust loads. The radial loads are imposed on the bearing assembly by the forces imposed on the shafts while the thrust loads are imposed on the bearing assemblies axially along the shafts by thrust plates or elements connected to the shaft between the shaft and the spindle adjacent the end frames of the machine. In accordance with prior art cutting machines, bronze bearing assemblies were utilized to provide a sliding journal bearing for the spindle shafts and the bearing assemblies included a fixed annular thrust load receiving surface for reacting thrust loads axially along the shaft adjacent the machine frame that were imposed on the bearing due to axial movement of the shaft and its associated blade carrying spindle. High friction loading was imposed on the thrust load receiving surfaces of such bearings, leading to failure of the bearings.
While lubrication schedules were specified by the manufacturer of such machines to maintain the bearing assemblies lubricated, frequent cleanings of the food cutting machinery utilizing high pressure sprays of cleaning fluid tended to remove lubricant from the bearing area which also resulted in premature bearing failure.
The bronze bearing assemblies in accordance with the prior art also resulted in higher friction drag on the rotating drive shafts due to the nature of the journal bearing surfaces, particularly when lubricant was scarce. Due to the open nature of the bronze type journal bearings used in accordance with the prior art, careful lubrication procedures were required to minimize flow of lubricant into the food cutting area. Although food grade lubricant is utilized in such bearings, modern standards for food preparation equipment tend to require minimum presence of lubricant in the food cutting area of such machines.
Early attempts to substitute a ball bearing assembly for the bronze journal bearings proved unsuccessful for a number of reasons. Primarily, fretting and corrosion problems between the outer periphery of the shafts and the inner race of the ball bearings lead to seizure between the shafts and the bearings that prevented axial removal of the shafts from the bearing assemblies. In food cutting machinery constructed in accordance with the prior art, removal of the shafts axially from the bearing assemblies is required to permit disassembly of the shafts, spindles and cutting blades during maintenance and repair operations. Due to the seizure problems, direct driving engagement between the shafts and the inner races of the bearings was impractical and there still remained the matter of reacting axial thrust loads imposed on the shaft into the inner race of the bearing assembly.
When standard sealed ball bearing assemblies were utilized, it was observed that high pressure cleaning sprays still penetrated the bearing seals which tended to remove lubricant from the bearings in spite of the presence of the sealed elements.
Thus, it became desirable to provide a low friction, shielded, sealed bearing assembly that could react radial and thrust loads while preventing direct impingement of cleaning sprays against the seal elements while minimizing thrust load friction at the bearing, and while avoiding fretting, corrosion and seizure problems between the shaft and bearing.
It also became highly desirable to provide a bearing assembly that could be readily adjustable within the machine frames both axially and radially to accommodate different shaft positions within the side frames and to permit precise adjustment of end play or clearances between the bearing thrust surfaces during set up of the shafts, cutting blades and spindles of the cutting machine.